In general, III-nitride compound semiconductors have a direct bandgap, which is capable of controlling wavelengths from visible to ultraviolet, and excellent physical properties of high thermal and chemical stability, high electron mobility, and high saturation electron velocity, as compared with the GaAs and InP-related compound semiconductors. With these properties, the III-nitrides have been widely applied to the optical devices such as light emitting diodes (LED), and laser diodes (LD) for visible light; the electronic devices for wireless and satellite communication systems; and other fields that exceed the limitations of the existing compound semiconductor. The emission characteristics of the III-nitrides depend on the active layer, consisted of InGaN, GaN, AlGaN or InAlGaN, and a p-type electrode layer, taking lights from the active layer.
However, the emission properties of III-nitrides are difficult in increasing quantum efficiency due to a large lattice mismatch and growth temperature difference between the active layer and the electrode layer. Particularly, in the case of using a sapphire substrate, the current crowding effects easily occur because of a structure that the n-type and p-type electrodes are located on the same plane. Furthermore, in the case of p-type GaN, the current crowding is happened to the high resistivity and low mobility, so that light emission and heat generation are not uniform, thereby deteriorating the characteristics of the light emitting diode. Accordingly, to improve the characteristics of the light emitting diode, there have been researched various device structures and manufacturing processes which can decrease the current crowding.